1. Field of the Invention
The present invention relates to an encapsulation method and leadframe for semiconductor packages and, more particularly, to an encapsulation method and leadframe for leadless semiconductor packages.
2. Description of the Related Art
Conventional encapsulation methods for packaging semiconductor devices are classified into two kinds. The first encapsulation method is applied to semiconductor packages with leads, as shown in FIG. 1. A plurality of dice are respectively mounted in cavities 11 of a leadframe 1, and are connected to the pins of the leadframe 1. The leadframe 1 has runner 12, and the runner 12 is connected to cavities 11 by sub-runners 13 and gates 14. Each gate 14 is an injection inlet between a sub-runner 13 and a cavity 11. Molding material is injected into the runner 12 and moves via the sub-runners 13 and the gates 14 to cavities 11 so as to package the dice in cavities 11. This encapsulation method requires space for the runner 12 and the sub-runners 13, thereby decreasing the number of dice within the leadframe area, and does not have high packaging efficiency.
The second encapsulation method is applied to leadless semiconductor packages, as shown in FIG. 2. A plurality of dice 22 are placed in a cavity 21. Molding material is injected into the cavity 21 to package the dice 22. Therefore, the number of dice within the leadframe is increased, and the cost of the leadframe can be decreased. However, the second method must use cutting equipment to cut the packaged semiconductor devices into individual pieces, and the cutting equipment is usually expensive. Therefore, the cost of the second method is high. Furthermore, after the semiconductor devices are cut, every one of the semiconductor devices must be transferred to a tray or a tube so that the steps of the second method are complex and the efficiency of the second method is low.
Besides, as shown in FIG. 3, each packaged semiconductor device 3 has no contact leads. Instead, device 3 has a plurality of conducting portions 31 for connection to a circuit board. When the leadless semiconductor device 3 is packaged, molding flash must not remain on the conducting portions 31. Therefore, during the packaging process, a film at the bottom of the semiconductor device 3 is needed to prevent molding flash from remaining on the conducting portions 31. Such a film increases the cost of the second method and degrades the efficiency.
On the other hand, the second method must utilize an upper mold and a lower mold to clamp the periphery of the leadframe 2, and the molding material is injected into the cavity 21 formed by the upper and lower molds. Because the cavity 21 is large, the upper and lower molds can only clamp the periphery of the leadframe 2. The middle portion of the cavity 21 cannot be clamped by the upper and lower molds. This will easily cause molding flash to remain on the conducting portions 31.
Therefore, it is desirable to provide a creative and improved encapsulation method and leadframe to overcome the above problems.